Topics

Shooting on-set monitors for post image insertion

Marty Brenneis
 

Some of you know me as a playback guy who comes in and syncs up the CRT with the camera so you don't get those ugly interference bars in the image.
Bloody LCD screens kind of killed that business but it is coming back.

Many times I get to set these days and the brain trust has still not decided what the graphic is, so they want to "greenscreen it and fix it in post".

I have been told many things by camera people about what they want to shoot, but I can tell that some of them have no real clue about the post process that will follow.
From my days at ILM I know how the process works when done in a photochemical pipeline. When we get to the new-fangled digital pipelines it seems there are many ways to work the problem.

I'd like to hear from some post people about what they like to see on the monitor screen so they can get a good image insertion with minimal work for roto and tracking.
Bright green, dark green, grey, black, grids, tracking triangles, a random movie playing? 

The thing that made ILM what it was was the close connection between camera acquisition people and post people. That is mostly gone these days, but places like CML allow for such discourse.

Thanks
Marty Brenneis
droid for hire
24frame.tv

Tony Quinsee-Jover
 

I always ask for a randomly patterned static green image.  Light green pattern on a darker green background, or the other way around. Not too bright (50% luminance and 30% Saturation in the frame) works well, (or thereabouts). The pattern doesn’t need to be anything clever, it’s only there to simplify planar tracking, and the two shades ideally want to be quite close together on the colour wheel – maybe only 10% luminance difference and of course exactly the same hue.  The two shades of green can be included in a single key, making for simple image replacement and retaining the ability to capture screen reflections and highlights. A grid (green on green) makes a good second choice.

 

Having said that, what I ask for and what I get are rarely the same.

 

A plain green screen will also work, but it can be harder to track in some situations, especially if there’s a lot of occlusion. Tracking marks (within the screen area ONLY please!) have to be painted out, which isn’t hard, but it’s a little extra work (especially, again, if there is much occlusion).

 

A 50% grey screen can be great for capturing reflections and highlights but requires loads of rotoscoping.

 

A black screen can sometimes prove impossible to track but allows the best-looking screen replacement and of course has to be fully rotoscoped.

 

Just my opinions, others are available.

 

All the above assumes planar tracking.  If the post house is going to use a point tracker, then the answers would be different.

 

Cheers,

Tony Quinsee-Jover

MD, HD Heaven, Birmingham, UK

 

From: cml-post-vfx-aces@... [mailto:cml-post-vfx-aces@...] On Behalf Of Marty Brenneis
Sent: 10 April 2018 07:22
To: cml-post-vfx-aces@...
Subject: [cml-post-vfx-aces] Shooting on-set monitors for post image insertion

 

Some of you know me as a playback guy who comes in and syncs up the CRT with the camera so you don't get those ugly interference bars in the image.
Bloody LCD screens kind of killed that business but it is coming back.

Many times I get to set these days and the brain trust has still not decided what the graphic is, so they want to "greenscreen it and fix it in post".

I have been told many things by camera people about what they want to shoot, but I can tell that some of them have no real clue about the post process that will follow.
From my days at ILM I know how the process works when done in a photochemical pipeline. When we get to the new-fangled digital pipelines it seems there are many ways to work the problem.

I'd like to hear from some post people about what they like to see on the monitor screen so they can get a good image insertion with minimal work for roto and tracking.
Bright green, dark green, grey, black, grids, tracking triangles, a random movie playing? 

The thing that made ILM what it was was the close connection between camera acquisition people and post people. That is mostly gone these days, but places like CML allow for such discourse.

Thanks
Marty Brenneis
droid for hire
24frame.tv

Tim Sassoon
 

Marty,

Nothing. Monitor turned off. At most, if the join from screen to bezel is really ambiguous, corner dots of any color. This is because we want to not lose any surface reflection the screen may have - especially important for smartphones. Tracking software is really good these days. Find out from VFX what tracker they use. Some, like Syntheyes, have a specific lens analysis routine.

The only time to use green is if there’s hair in the foreground. If it’s just a thumb or other hard-edged object, most VFX artists today would prefer to rotoscope the edge rather than remove the green. And there’s a chance they may feel that way about hair, too.


Tim Sassoon
SFD
Venice, CA


On Apr 9, 2018, at 11:21 PM, Marty Brenneis <marty@...> wrote:

I have been told many things by camera people about what they want to shoot, but I can tell that some of them have no real clue about the post process that will follow.

Stu Willis
 

Tony did a great job of listing the different approaches. 

That said I tend to err on the side of Tim's advice - nothing is best. Monitors, at least for now, are flat regular shapes with (often) defined borders - prefect for planar trackers. Markers on the corners will help.

Having reflections at the cost of roto + tracking is worth it. Put another way, the cost of roto + tracking is far smaller than than cost (effort, money, skills) of believably faking reflections. Tracking + roto tools have come a long way. Planar trackers like Mocha are also able to track and morph roto shapes, too. 

The main downside is the lack of interactive light from the device itself. You can fake it with some selective grading with selective roto work... But, in my experience, most people won't notice its absence.



On 12 April 2018 at 14:32, Tim Sassoon via Cml.News <tsassoon=aol.com@...> wrote:
Marty,

Nothing. Monitor turned off. At most, if the join from screen to bezel is really ambiguous, corner dots of any color. This is because we want to not lose any surface reflection the screen may have - especially important for smartphones. Tracking software is really good these days. Find out from VFX what tracker they use. Some, like Syntheyes, have a specific lens analysis routine.

The only time to use green is if there’s hair in the foreground. If it’s just a thumb or other hard-edged object, most VFX artists today would prefer to rotoscope the edge rather than remove the green. And there’s a chance they may feel that way about hair, too.


Tim Sassoon
SFD
Venice, CA


On Apr 9, 2018, at 11:21 PM, Marty Brenneis <marty@...> wrote:

I have been told many things by camera people about what they want to shoot, but I can tell that some of them have no real clue about the post process that will follow.




--

---
stuart willis
editor + post
melbourne

Rick Gerard
 

The only time I think tracking markers are useful when you are doing motion capture on an actor. Putting tracking markers on any kind of fixed geometry just adds time to the post process. The more reflective the surface and the more the action crosses the markers the more time it adds.

I have done a lot of screen replacement recently with footage from many different sources and the easiest by far, even if you have roto to do, is NO tracking markers because they foul up the reflections make the edges of any roto you need to do or keying more difficult. I have successfully pulled keys from dark green. Turning off the display also works. It is very easy to simulate light coming from the screen with light wrap when the subject is close to the screen. If the subject is a little farther away you can use supplemental lighting on set.

When I am shooting I prepare a half dozen different gray screens from about 10% brightness to 80%, load each onto the screen and then check for reflections. Many times you get the reflections you need with a 40% or 50% gray screen and this still gives you a fair amount of practical light. You just have to pay attention when you are shooting.

As long as you have some kind of geometric edge like a bezel covering most of 3 sides you can get an accurate track using Mocha without any markers and the process is very easy and takes very little time.

When I am shooting green screen with moving cameras I also do not use tracking markers. Instead I put some green boxes in the shot that so Camera Tracking software can find some planes to track. The track is easier to do and more accurate by far than trying to figure out the camera moves with a bunch of X’s on the wall. Any garbage matting or minor roto required to completely remove the background because of the boxes only takes a few seconds. IMHO, tracking markers are more trouble than they are worth on most shots. 



Rick Gerard
DP/VFX Supervisor
MovI Pro / Licensed Commercial Pilot Fixed Wing and UAV
Northern CA